Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 767–770
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Raman spectroscopy of coal component of Late Permian coals from Southern China Shaoqing Wang ⇑, Hongfei Cheng, Di Jiang, Fan Huang, Shen Su, Haipeng Bai College of Geoscience and Surveying Engineering, China University of Mining and Technology (Beijing), D11, Xueyuan Road, Beijing 100083, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Barkinite has higher degree of
disorder in chemical structure than vitrinite. Nine bands were assigned from the Raman spectra when deconvolution. Two typical bands, G and D1, were assigned for barkinite.
a r t i c l e
i n f o
Article history: Received 24 March 2014 Received in revised form 27 May 2014 Accepted 3 June 2014 Available online 12 June 2014 Keywords: Coal Barkinite Vitrinite Raman spectroscopy Curve-fitting
a b s t r a c t The chemical structural characterization of four samples (M-1, M-5, VS, and BaS) from Southern China was studied by Raman spectroscopy with curve-fitting analysis. Several Raman parameters, e.g., full width at half maximum (FWHM) and intensity ratio (ID1/IG), were obtained. Vitrinite (VS) and barkinite (BaS) were separated from the same coal sample, separately. The results showed that nine bands were assigned from the Raman spectra. Two typical bands, G and D1, have broad peaks, which showed that all the samples have poor order in chemical structure. Barkinite has higher disorder in chemical structure than vitrinite. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Raman spectroscopy is sensitive to crystalline and amorphous structure of samples, which has been widely used for obtaining information about the microstructure of carbon-based materials [1]. Some parameters derived from Raman spectral can provide information on the degree of ordering and crystallinity in carbonaceous materials [1]. Raman spectra from coal have bands
⇑ Corresponding author. Tel.: +86 10 6233 1657. E-mail address: [email protected] (S. Wang). http://dx.doi.org/10.1016/j.saa.2014.06.003 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
associated with amorphous and graphitic carbon [2]. So, the Raman spectroscopy has been employed to characterize coal structure, especially the change of Raman parameters with the maturity of coals [2–4], and coal char structure [5]. Recently, detailed information on the characterization of Raman spectroscopy of coal was reviewed [6]. The correlation between the Raman spectra and the structure of carbon materials [7] and graphitization products [8] was discussed, especially the development of the first- and second-order Raman spectra with the coalification or graphitization. Meanwhile, the Raman spectroscopy was also a good tool to determine the characterization of maceral concentrates. Zerda et al. [9] applied for Raman spectroscopy to discuss the Raman
768
S. Wang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 767–770
characterization of the samples where the vitrinite and inertinite were separated. The Raman spectral features of individual coal macerals (collotelinite, fusinite, and macrinite) were studied using micro-Raman spectroscopy by Guedes et al. [7] and that of carbonized semifusinite and fusinite was also discussed by Morga [10]. In general, the first-order (G band) and second-order regions (D1 band) are presented in the Raman spectra of carbonaceous materials. The first-order region is typical range, especially for perfect graphite that has one band at about 1580 cm 1 (G band) [10]. However, for highly disordered carbon material, the additional bands are also usually appeared around 1150 cm 1 (D4 band), 1350–1380 cm 1 (D1 band), 1500–1550 cm 1 (D3 band), and 1620 cm 1 (D2 band) [11], which resulted from the defects in the microcrystalline lattices. In addition, three bands (1540 cm 1, 1465 cm 1, and 1380 cm 1) were suggested between the G and D1 band when studying brown coal chars [12] as well as the other bands, 1230–1260 cm 1, 1060–1090 cm 1, and 1680 cm 1, were also introduced by Li et al. [12] and Guedes et al. [7]. Barkinite has been classified as a liptinitic maceral in Chinese nomenclature and some papers have introduced the petrographic and structural characteristics of barkinite [13–29], especially in some international journals [13–32]. However, barkinite has not yet been recognized as a maceral by organizations such as the International Committee for Coal and Organic Petrology (ICCP) or The Society for Organic Petrology (TSOP). Hower et al. [33] also suggested that it was more appropriate to use the term ‘‘component’’ instead of ‘‘maceral’’ for barkinite. In previous works, the structural characteristics of barkinite have been studied by some analytical methods, such as FT-IR, and 13C NMR [14,16,22– 24,27,28]. The most distinct feature of barkinite is its rich aliphatic structures concentration [34,22]. However, the information on the features of Raman spectrum of barkinite has not been obtained. The optical transitional feature between barkinite and vitrinite has been reported [19], but what is difference of Raman spectra between barkinite and vitrinite? So, in the present work, the objectives were to study the characterization of Raman spectra of samples and to further make a comparison with the difference of Raman spectrum for barkinite and vitrinite. Samples and experimental
ion laser (514 nm) with the experiment power of 50 mW at a nominal resolution of 1 cm 1 in the range between 100 and 4000 cm 1, the entrance slit is 50 lm. The data acquisition time for each spectrum was 30 s. To obtain further data, peak separation and semiquantitative calculation of Raman spectroscopy were carried out using the curve-fitting program of PeakFit software. For each Raman spectrum, the selected regions were baseline-linearized and an area normalization before curve-fitting. To have a good initial estimate of the frequency and intensity of peaks, it is necessary to determine the number of peaks in a given region. The detailed process for curve-fitting can maybe be found elsewhere [24]. Results and discussion Main characteristics of the selected samples Table 1 listed the results of petrographic, proximate and ultimate analyses of the samples. The basic information on elemental composition is as follows: 5.57–6.91 (wt.%) hydrogen ranges, on a dry-ash-free basis (daf), 0.81–1.01 H/C atomic ratio ranges. For proximate analysis, the noticeable characterization is high volatile matter yield (38.79–62.16, wt.%, daf). BaS has the highest volatile matter yield (>60%). A similar result has been obtained by other authors [15,25,26]. Hsieh [25] reported that ‘‘lopinite’’ has a high volatile matter yield, up to 37 (wt.%, daf), different from other humic coals. For macerals composition, the vitrinite and liptinite are main two macerals, almost over 80.0%. For M-5, the barkinite content reaches to 67.3%, and for M-1, the vitrinite content is up to 74.5%. According to the values of maximum vitrinite reflectance, the ranks of the samples are high volatile bituminous B. Raman characterization of the coals The Raman spectra of the coal samples in the range of 1000– 1800 cm 1 are presented in Fig. 1. Two peaks with maxima intensity at around 1350–1370 cm 1 and almost 1590 cm 1, separately, are exhibited, corresponding to the D1 and G bands of disordered graphite. In the earlier works [40,41] on carbon material has shown that Raman spectra of graphite and diamond have two Raman bands at 1581 cm 1 and 1332 cm 1, respectively. For perfect
Sample preparation Two coal samples (M-1 and M-5) were collected from the Mingshan (MS) coal mine in the South of China. The individual macerals (BaS and VS) were separated from MS coal by combining hand picking and density gradient centrifugation (DGC) method. The sample was ground to 200 mesh and the demineralization of coal was carried out by HF and HCl solutions with HClO4. A detailed procedure of macerals separating was described in other work [35]. The purities of both barkinite and vitrinite were measured in light microscopy. The purities of both barkinite (BaS) and vitrinite (VS) are 96%. Reflectance reported was the mean value of 100 measurements. Maceral compositions were determined in the State Key Laboratory of Coal Resources and Safe Mining (Beijing, China). Proximate analysis and ultimate analysis were carried out following methods GB/T 212–2008 [36], GB/T 476-2008 [37], GB/T 214-2007 [38], and GB/T 215-2003 [39], separately. Raman spectroscopy The samples were placed and oriented on the stage of a Renishaw 100 Raman spectrometer with microscopy, equipped with 10 and 50 objectives. Raman spectra were excited by an argon
Table 1 The general information on the samples used. M-5
VS
BaS
Elemental composition (wt.%, daf) C 80.94 H 5.57 N 1.48 St 1.07 a O 10.94 H/C 0.83
M-1
79.77 6.14 1.55 1.07 11.48 0.92
85.84 5.80 1.73 0.41 6.22 0.81
81.59 6.91 1.57 0.11 9.82 1.01
Proximate analysis (wt.%) M(ad) 1.73 A(d) 29.63 VM(daf) 38.79
1.02 8.15 52.80
1.27 1.60 43.78
0.71 0.97 62.16
Petrographic composition (vol.%) V 74.5 Ba 1.2 OL 4.5 I 19.8 Ro (%) 0.69
23.8 67.3 1.0 7.8 0.70
>96 0 0
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Raman spectroscopy of coal component of Late Permian coals from Southern China Shaoqing Wang ⇑, Hongfei Cheng, Di Jiang, Fan Huang, Shen Su, Haipeng Bai College of Geoscience and Surveying Engineering, China University of Mining and Technology (Beijing), D11, Xueyuan Road, Beijing 100083, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Barkinite has higher degree of
disorder in chemical structure than vitrinite. Nine bands were assigned from the Raman spectra when deconvolution. Two typical bands, G and D1, were assigned for barkinite.
a r t i c l e
i n f o
Article history: Received 24 March 2014 Received in revised form 27 May 2014 Accepted 3 June 2014 Available online 12 June 2014 Keywords: Coal Barkinite Vitrinite Raman spectroscopy Curve-fitting
a b s t r a c t The chemical structural characterization of four samples (M-1, M-5, VS, and BaS) from Southern China was studied by Raman spectroscopy with curve-fitting analysis. Several Raman parameters, e.g., full width at half maximum (FWHM) and intensity ratio (ID1/IG), were obtained. Vitrinite (VS) and barkinite (BaS) were separated from the same coal sample, separately. The results showed that nine bands were assigned from the Raman spectra. Two typical bands, G and D1, have broad peaks, which showed that all the samples have poor order in chemical structure. Barkinite has higher disorder in chemical structure than vitrinite. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Raman spectroscopy is sensitive to crystalline and amorphous structure of samples, which has been widely used for obtaining information about the microstructure of carbon-based materials [1]. Some parameters derived from Raman spectral can provide information on the degree of ordering and crystallinity in carbonaceous materials [1]. Raman spectra from coal have bands
⇑ Corresponding author. Tel.: +86 10 6233 1657. E-mail address: [email protected] (S. Wang). http://dx.doi.org/10.1016/j.saa.2014.06.003 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
associated with amorphous and graphitic carbon [2]. So, the Raman spectroscopy has been employed to characterize coal structure, especially the change of Raman parameters with the maturity of coals [2–4], and coal char structure [5]. Recently, detailed information on the characterization of Raman spectroscopy of coal was reviewed [6]. The correlation between the Raman spectra and the structure of carbon materials [7] and graphitization products [8] was discussed, especially the development of the first- and second-order Raman spectra with the coalification or graphitization. Meanwhile, the Raman spectroscopy was also a good tool to determine the characterization of maceral concentrates. Zerda et al. [9] applied for Raman spectroscopy to discuss the Raman
768
S. Wang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 767–770
characterization of the samples where the vitrinite and inertinite were separated. The Raman spectral features of individual coal macerals (collotelinite, fusinite, and macrinite) were studied using micro-Raman spectroscopy by Guedes et al. [7] and that of carbonized semifusinite and fusinite was also discussed by Morga [10]. In general, the first-order (G band) and second-order regions (D1 band) are presented in the Raman spectra of carbonaceous materials. The first-order region is typical range, especially for perfect graphite that has one band at about 1580 cm 1 (G band) [10]. However, for highly disordered carbon material, the additional bands are also usually appeared around 1150 cm 1 (D4 band), 1350–1380 cm 1 (D1 band), 1500–1550 cm 1 (D3 band), and 1620 cm 1 (D2 band) [11], which resulted from the defects in the microcrystalline lattices. In addition, three bands (1540 cm 1, 1465 cm 1, and 1380 cm 1) were suggested between the G and D1 band when studying brown coal chars [12] as well as the other bands, 1230–1260 cm 1, 1060–1090 cm 1, and 1680 cm 1, were also introduced by Li et al. [12] and Guedes et al. [7]. Barkinite has been classified as a liptinitic maceral in Chinese nomenclature and some papers have introduced the petrographic and structural characteristics of barkinite [13–29], especially in some international journals [13–32]. However, barkinite has not yet been recognized as a maceral by organizations such as the International Committee for Coal and Organic Petrology (ICCP) or The Society for Organic Petrology (TSOP). Hower et al. [33] also suggested that it was more appropriate to use the term ‘‘component’’ instead of ‘‘maceral’’ for barkinite. In previous works, the structural characteristics of barkinite have been studied by some analytical methods, such as FT-IR, and 13C NMR [14,16,22– 24,27,28]. The most distinct feature of barkinite is its rich aliphatic structures concentration [34,22]. However, the information on the features of Raman spectrum of barkinite has not been obtained. The optical transitional feature between barkinite and vitrinite has been reported [19], but what is difference of Raman spectra between barkinite and vitrinite? So, in the present work, the objectives were to study the characterization of Raman spectra of samples and to further make a comparison with the difference of Raman spectrum for barkinite and vitrinite. Samples and experimental
ion laser (514 nm) with the experiment power of 50 mW at a nominal resolution of 1 cm 1 in the range between 100 and 4000 cm 1, the entrance slit is 50 lm. The data acquisition time for each spectrum was 30 s. To obtain further data, peak separation and semiquantitative calculation of Raman spectroscopy were carried out using the curve-fitting program of PeakFit software. For each Raman spectrum, the selected regions were baseline-linearized and an area normalization before curve-fitting. To have a good initial estimate of the frequency and intensity of peaks, it is necessary to determine the number of peaks in a given region. The detailed process for curve-fitting can maybe be found elsewhere [24]. Results and discussion Main characteristics of the selected samples Table 1 listed the results of petrographic, proximate and ultimate analyses of the samples. The basic information on elemental composition is as follows: 5.57–6.91 (wt.%) hydrogen ranges, on a dry-ash-free basis (daf), 0.81–1.01 H/C atomic ratio ranges. For proximate analysis, the noticeable characterization is high volatile matter yield (38.79–62.16, wt.%, daf). BaS has the highest volatile matter yield (>60%). A similar result has been obtained by other authors [15,25,26]. Hsieh [25] reported that ‘‘lopinite’’ has a high volatile matter yield, up to 37 (wt.%, daf), different from other humic coals. For macerals composition, the vitrinite and liptinite are main two macerals, almost over 80.0%. For M-5, the barkinite content reaches to 67.3%, and for M-1, the vitrinite content is up to 74.5%. According to the values of maximum vitrinite reflectance, the ranks of the samples are high volatile bituminous B. Raman characterization of the coals The Raman spectra of the coal samples in the range of 1000– 1800 cm 1 are presented in Fig. 1. Two peaks with maxima intensity at around 1350–1370 cm 1 and almost 1590 cm 1, separately, are exhibited, corresponding to the D1 and G bands of disordered graphite. In the earlier works [40,41] on carbon material has shown that Raman spectra of graphite and diamond have two Raman bands at 1581 cm 1 and 1332 cm 1, respectively. For perfect
Sample preparation Two coal samples (M-1 and M-5) were collected from the Mingshan (MS) coal mine in the South of China. The individual macerals (BaS and VS) were separated from MS coal by combining hand picking and density gradient centrifugation (DGC) method. The sample was ground to 200 mesh and the demineralization of coal was carried out by HF and HCl solutions with HClO4. A detailed procedure of macerals separating was described in other work [35]. The purities of both barkinite and vitrinite were measured in light microscopy. The purities of both barkinite (BaS) and vitrinite (VS) are 96%. Reflectance reported was the mean value of 100 measurements. Maceral compositions were determined in the State Key Laboratory of Coal Resources and Safe Mining (Beijing, China). Proximate analysis and ultimate analysis were carried out following methods GB/T 212–2008 [36], GB/T 476-2008 [37], GB/T 214-2007 [38], and GB/T 215-2003 [39], separately. Raman spectroscopy The samples were placed and oriented on the stage of a Renishaw 100 Raman spectrometer with microscopy, equipped with 10 and 50 objectives. Raman spectra were excited by an argon
Table 1 The general information on the samples used. M-5
VS
BaS
Elemental composition (wt.%, daf) C 80.94 H 5.57 N 1.48 St 1.07 a O 10.94 H/C 0.83
M-1
79.77 6.14 1.55 1.07 11.48 0.92
85.84 5.80 1.73 0.41 6.22 0.81
81.59 6.91 1.57 0.11 9.82 1.01
Proximate analysis (wt.%) M(ad) 1.73 A(d) 29.63 VM(daf) 38.79
1.02 8.15 52.80
1.27 1.60 43.78
0.71 0.97 62.16
Petrographic composition (vol.%) V 74.5 Ba 1.2 OL 4.5 I 19.8 Ro (%) 0.69
23.8 67.3 1.0 7.8 0.70
>96 0 0
